Plastic coated metallic foams

ABSTRACT

The properties of articles fabricated from foamed metals (such as foamed aluminum) are enhanced by coating surfaces thereof with plastic materials, e.g., acrylonitrile-butadiene-styrene polymers. For example, the plastic coating improves the physical properties, and enables the article to be joined to another foamed metal article, or to a metal sheet, wire, glass, rock, or other material. The organic coat gives improved strength to such joint.

United States Patent 1 Jarema et a1.

1 *Oct. 1, 1974 1 1 PLASTIC COATED METALLIC FOAMS [75] Inventors:Chester P. Jarema, Detroit; Leonard M. Niebylski, Birmingham, both ofMich.

[73] Assignee: Ethyl Corporation, Richmond, Va.

[ Notice: The portion of the term of this patent subsequent to Nov. 2,1988, has been disclaimed.

[22] Filed: June 14, 1972 [21] Appl. No.: 262,511

Related U.S. Application Data [60] Division of Ser. No. 155,102, June21, 1971, Pat. No. 3,707,401, which is a continuation-in-part of Ser.No. 774,756, Nov. 12, 1968, Pat. No. 3,617,364.

[52] U.S. Cl.. 117/132 B, 117/132 BE, 117/132 BF, 117/132 BS, 117/132 C,117/132 CF, 161/159, 161/160, 161/161, 161/162, 111/21 [51] Int. Cl1332b 15/08 [58] Field of Search 117/132; 161/159, 160, 161/161, 162

['5 6] References Cited UNITED STATES PATENTS 3,268,304 8/1966 Vaught etal. 29/183 3,499,819 3/1970 Lewis 161/161 3,617,364 11/1971 Jarema eta1. 161/160X Primary Examiner-William D. Martin Assistant Examiner-HarryJ Gwinnell Attorney, Agent, or FirmDonald L. Johnson; Robert A. Linn;Joseph D. Odenweller 5 7 ABSTRACT 4 Claims, 3 Drawing Figures PATENIEDBHH 4 asaaoao FIGURE. l

FIGURE 3 PLASTIC COATED METALLIC FOAMS This application is a division ofapplication Ser. No. 155,102, filed June 21, 1971, now U.S. Pat. No.3,707,401, which in turn is a continuation-in-part of application Ser.No. 774,756, filed Nov. 12, 1968, now U.S. Pat. No. 3,617,364.

BACKGROUND OF THE INVENTION Foamed metals have been described in theprior art, see, for example, U.S. Pat. Nos. 2,895,819; 3,300,296; and3,297,431. In general, such foams are prepared by adding a gas-evolvingcompound to a molten metal, and heating the resultant mixture todecompose the gas-forming compound to prepare blowing gas. The gascauses the metal to foam by expansion. After blowing, the resultant bodyis cooled to produce a foamed solid. Such gas-forming solid may be ametal hydride such as TiH ZrI-I or magnesium, aluminum, or lithiumhydride, U.S. Pat. No. 2,983,597.

SUMMARY OF THE INVENTION It has been discovered that foamed metal bodiesproduced by methods such as generally described and referred to aboveare materially enhanced by coating them with a plastic material.

For example, the coating adds strength, especially in such cases wherethe coating is imbibed into the surface of the metal by filling thecavities on the surface. (Such cavities can be relatively large tomicroscopic in size.) Second, such coatings can provide a means forattaching a foamed metal to another body. This is done by melting theplastic coating, pressing it to the surface to be attached so the moltenplastic sticks to both surfaces to be bonded, and then cooling.Furthermore, the coating can be decorative. Moreover, the surface can bealtered to confer different properties by a proper choice of the coatingpolymer. Thus, to make a more or less slippery" surface a film of Tefloncan be fused on the surface of the foamed body. To make the body elasticor springy, a rubber can be fused thereon. To make the surface sticky,an adhesive can be used. The adhesive layer can be covered forprotection prior to use by a sheet of paper, cloth, or the like.

In addition, the plastic coating can markedly improve other properties.Thus, coated plastics of this invention have less tendency to absorbliquids such as water. Compressive, flexural, shear, and tensilestrength are improved; friability is decreased.

FIG. 1, which is not to scale, illustrates this invention. In FIG. 1,ABCD represents a section through a foamed metal body, said sectionbeing taken by cuts along AB, BD, and CD. The circles and partialcircles within ABCD represent cross sections of bubbles in the foamedsubstrate. The bubbles were made by blowing gas during the foamingprocess. As can be seen, these bubbles can be of equal or differentsizes, wholly separated, or joined together. It is not necessary thatthe bubbles be spherical as shown.

As illustrated, there are three cavities in Surface AC of the foamedsubstrate (in the illustrated section). Of course, these cavities can beformed during the blowing process and the number of cavities can be moreor less in any given section.

ACFE represents a layer of plastic on Surface AC of the foamedsubstrate. As illustrated, the plastic layer extends into the cavitiesin the coated surface. This invention covers surfaces having cavitieswhich are partially filled, substantially filled, or entirely filled.

FIG. 2 is a cross section of foamed plastic coated formed metal.

FIG. 3 is a cross section of a fiber mat reinforced plastic coatedfoamed metal body.

DESCRIPTION OF PREFERRED EMBODIMENTS The plastics which can be used tocoat foamed metals according to this invention can be chosen from a widevariety of materials.

The following illustrative but nonlimiting outline serves to demonstratewhat types of plastics can be used in polymer-coated foamed metalsprovided by this invention.

A. Derivatives of Natural Products Cellulose nitrate, cellulose acetate,cellulose acetate-butyrate, ethyl-cellulose, rubber, vulcanized rubber,chlorinated rubber.

B. Phenolic Materials Bakelite, phenol-formaldehyde novolacs andresoles, A-stage, B-stage, and C-stage resins.

C. Other Formaldehyde-based Polymers Condensation products offormaldehyde with urea or melamine.

D. Alkyd Resins Condensation products of alcohols such as glycerine,ethylene glycol, diethylene glycol or pentaerythritol with succinic,adipic, citric, sebacic, azelaic, phthalic, terephthalic, or maleicacid.

E. Epoxides and Phenoxy Resins Alkaline condensation product ofepichlorohydren with bisphenol A.

F. Silicones G. Furan Polymers Polymers of furfuryl alcohol or furfural,furfuralphenolics, urea-formaldehyde resins containing furfuryl alcohol.

H. Nylons Condensation products of diacids with diamines.

I. Polyamides Nylon-6 J. Polyurethanes 'Reaction products oftoluene-2,4-diisocyanate and polyhydric alcohols K. Thiokols L.Polycarbonates Produced by phosgenation of dihydroxy aromatics such asbisphenol A.

M. Polysulfones Reaction products of bisphenol A andbis-(pchlorophenyl)sulfone.

N. Chlorinated Polyester Produced by polymerizing 3,3-bis(chloromethyl)-loxacyclobutane in liquid S0 with BF;,.

0. Acetal Polymers Delrin, Celcon P. Polyphenylene Oxide Q. PolyimidesProduced by condensation of dianhydrides such as pyromellitic anhydrideand polyamines such as 4,4'-diaminodiphenyl ether.

R. Polyxylenes and Polyoxyethylenes S. Polyolefins Polyethylene,polypropylene, isotactic poly-1- butene, copolymers of ethylene andvinyl acetate, methyl acrylate, propylene, and acrylic acid. T.Polystyrene U. Vinyl Polymers Polyvinyl chloride, polymers ofunsaturated esters such as methyl methacrylate, allyl esters, ethylmethacrylate, vinyl acetate, copolymers of vinyl chloride and vinylidenechloride, polyvinyl'acetals. V. Fluorinated Ethylene-propylene,Tetrafluoroethylene and Related Fluorinated Materials W. Poly (alkylvinyl ethers), Polycarbazole, and

Polyvinylpyrollidones The plastic or polymeric coating agent(s) need notbe pure but in many instances are advantageously admixed with othermaterials. Thus, stabilizers, antioxidants, antiozonants, dyes, fillers,anti-static agents, anti-tack and slip agents, bacteriostats,brighteners, flame retardants, U.V. absorbers, and plasticizers can beused in the plastic or polymeric coats. For examples of such materialsknown in the art one can refer to tables in the 1968 edition of ModernPlastics Encyclopedia, McGraw Hill, Inc., New York, NY. Such tables (inthat publication) as those beginning on (a) page 503 (antioxidants) (b)page 500 (antistatic agents) page 496 (colorants) (d) page 491 (organicperoxides) (2) page 466 (plasticizers) (1) page 494 (solvents) (g) page510 (stabilizers) (h) page 508 (ultraviolet absorbers) are incorporatedby reference herein as if fully set forth. In addition, the plastic canbe mixed with other substances such as silicon carbide, ground glass, orsimilar substance, to render the coating layer abrasive or non-skidding.

The organo-polymers can be employed singly or in combination. When usedin combination, two, three, four or more of the above types of resinscan be variously combined. For example, the coat can be a more or lesshomogeneous mixture of plastics or two or more plastics can be added tothe foamed body in successive layers. Thus, laminar coats are anembodiment of the invention.

For example, the use of successive coats can .form bodies havingimproved properties and/or bodies having acceptable properties at lowercosts. Thus, the foamed metal can be first treated with a resinousmaterial which seeps into the cavities on the surface. Moreparticularly, this first coat can, for example, be applied as a liquid,such as a solution of a polymer in an organic solvent. Afterwards, thesolvent which facilitates seepage into the pores of the metal foam isthen allowed to evaporate, leaving the polymer coat on the foam.Alternatively, the first treatment can be with a monomer (or solution,emulsion, or suspension thereof) followed by polymerization of themonomer on (and in the surface cavities) of the foam. If the monomer isapplied together with an organic solvent, the solvent can be removedeither before or after the polymerization, as desired. Monomers andpolymers can be added by spraying, dipping or rolling.

Continuing the building of a laminar coat, other layers of the same ordifferent polymeric materials can be overlayed on the first coat.

In addition to polymeric materials, other types of substances can beoverlayed on the first layer.

Thus, for example, one or more layers of a plastic, such as aphenol-formaldehyde resin, can be applied to a foamed aluminum sheet.Next, a sheet of aluminum foil is bonded to the plastic coating, andthen (optionally) overlayed with another layer of plastic. Next, a paperis bonded to the article which paper optionally has a decorative designon the upward surface. The paper is then coated with a transparent,resistant plastic coat which protects the paper design from H O, air,etc. The resultant foamed sheet is useful as a building panel sandwichwherein the foamed aluminum portion provides lightweight, structuralstrength and the coated paper surface yields an aesthetically pleasingdecorative effect. Such sandwich composite can be used for interior orouter walls.

The layers of materials built up on a coated, foamed metal body of thisinvention need not be wholly integral. For example, such layers built upon the coated surface can be a plastic foam. The coated surface providesa better bond between the foamed plastic and the foamed metal.

Thus, for example, a relatively flat surface of a foamed metal sheet iscoated with a polymeric coat which is imbibed into the foam surface andforms a relatively smooth surface on the foamed body. This is thenoverlayed with a tacky overcoat of adhesive material so that theadhesive surface is exposed.

Next, (temporary, if desired) sides are provided around the metal sheetso said sheet forms with the sides, an open box-like structure with theadhesive surface being exposed in the box. (In other words, the bottomof the box-like structure is the foamed metal sheet.) Then, a foamableplastic composition is placed on the adhesive surface to the desireddepth, the sides serving to confine the foamable composition so there isminimal spillage. Thereafter, the plastic composition is allowed to foamand the adhesive surface provides a bond between the plastic and metalfoams. The plastic foam can be flexible, rigid, or semi-rigid asdesired.

FIG. 2 shows a cross section of a foamed plastic coating on a foamedmetal body. The plastic foam has penetrated the exposed pores of thefoamed metal.

It is not necessary to pre-coat the foamed metal with an adhesive beforeapplying the foamed plastic coating. The foamed plastic coating can beapplied by merely placing a foamable plastic composition directly on thefoamed metal surface and allowing it to foam. This is illustrated by thefollowing examples.

EXAMPLE 1 A piece of foamed aluminum (15 pounds per cubic foot) wassectioned to provide a surface with a large number of open pores. Afreshly prepared foamable polyurethane solution was poured on thesectioned surface (a mixture of 18 parts toluene diisocyanate, 8.8 partstrichloromethane, 0.12 part trimethyl piperazine, 0.1 part dibutyl tinlaurate, and 27 parts of a pentaerythritol-propylene oxide condensatewith a molecular weight of 450). After a few seconds the compositionfoamed to a depth of about 1 inch, providing a foamed aluminum panelwith an insulating layer of polyurethane foam integrally bonded to it.

EXAMPLE 2 A piece of sectioned foamed aluminum slab was coated to adepth of about 0. 125 inch with expandable polystyrene beads (DyliteF40, Koppers Company, lnc.). A flat plate was positioned 1 inch abovethe sectioned aluminum surface. Steam was passed between the foamedaluminum and the flat plate, causing'the polystyrene beads to expand,filling the void between the foamed aluminum surface and the flat plate.On expanding, the beads fused, resulting in a foamed aluminum panelcoated with an insulating layer of polystyrene foam. The polystyrenefoam was bonded tightly to the foamed aluminum surface principally dueto the physical penetration of the fused polystyrene into the surfacepores.

" These composite plastic and metal foams have many desirable utilities.Thus, they can be used in the walls of vehicular compartments. When soused, the metal foam is outside while the plastic foam is on the inside.With such configuration, the metal foam can pick up much shock shouldthere be an impact. The plastic foam on the inside has more give thanthe metal foam, and it better protects freight or passengersinadvertently jostled against the compartment walls during impact.

Moreover, composite plastic metal foams can be used as flooring. in thisinstance, the foamed metal provides structural strength. The plasticfoam adherent thereon is a built-in pad for carpeting. If desired, theplastic foam surface can have the carpeting pre-bonded thereto, and/or,non-coated surfaces of the metal foam body can have tongues and grooves(or some other surface configuration) provided to facilitate laying.

Of course, more than one surface of the metal foam can have a plasticfoam bonded thereto. Thus, for example, opposing surfaces can beprovided with an adherent plastic foam to form a sandwich-likestructure.

Illustrative but non-limiting plastic foams which can be bonded to ametal foam according to this invention are polystyrene (expanded beads),polyurethanes, and vinyl-containing foams such as described in Alzner,et al., and Klopfer, US. Pat. Nos. 3,338,845, and 3,338,846,respectively.

As illustrated above, polymeric coats applied to foamed metals accordingto this invention can be used as bonding agents to bond other materialsto a foamed metal article. According to one embodiment of thisinvention, the material so bonded need not provide a uniform surface.Thus, for example, a polymeric coat which is meltable can be applied toa surface of the foamed metal article. This can then be melted to form atacky surface. Into this, crushed rock can be embedded and the surfacethen cooled to form a foamed metal article having an irregular surfaceprovided by the crushed rock coat. These articles provide a new artisticmedium. Moreover, by varying the colors of the crushed rock, foamedmetal sheets can provide an extremely eye-pleasing wall unit. Asdesired, the color pattern of such curtain walls can be chosen toprovide a checkerboard, variegated, mosaic, or combined effect.

Curtain walls and other structural units made from plastic coated metalfoams according to this invention need not have surfaces unaffected byatmospheric or environmental conditions. In fact, this inventionencompasses embodiments where changes due to the environment are usedadvantageously. Thus, one embodiment of this invention comprises afoamed metal structural unit having a plastic coating thereon containinga phosphorescent or fluorescent material. Such structural units glow inthe dark after being exposed to light or fluoresce. Compounds such asacridine dyes, Rhodamine B and Rhodamine 66 as well as other materialsdiscussed in Kirk-Othmer's Encyclopedia of Chemical Technology, 2ndEdition, (in the section under Luminescent Materials) can be used.

In addition, electrically conducted wires can be embedded into theplastic layer attached to the foamed substrate. This provides a curtainwall panel which can be used to heat a room by radiant heat whenelectric current is called to flow through the resistance wires.

Similarly, materials which change color upon exposure to differentamounts of moisture can be stuck in the plastic coat and exposed to theenvironment. Salts such as cobaltous chloride and bromide can be used inthis manner.

As mentioned previously, the plastic coating can be applied to the metalfoam as a solution of a polymer in an organic solvent. Likewise,colloidal suspensions, called sols, of the polymer in a liquid mediumcan be employed in a similar manner. Useful solvents include aromatichydrocarbons such as benzene, toluene, and the like; alcohols such asmethanol, ethanol, isobutano], and the like; ketones such as acetone,methylethyl ketone, diethyl ketone, and the like; ethers such astetrahydrofuran, dioxane, diethyl ether, and the like; halohydrocarbonssuch as methylene chloride l,l,ltrichloroethane, perchloroethane, andthe like. Sols can be readily prepared in water. Methods of makingsuchsolutions and sols are well known. Examples of plastics that can beapplied in this manner include acrylonitrile-butadiene-styreneterpolymer (ABS resin), polyethylene, polyesters such as phthalicacid-glycol esters, polyvinyl chloride, and the like, including thosepreviously listed. The following examples illustrate the application ofa plastic coating using the above process.

EXAMPLE 3 A solution of ABS resin in tetrahydrofuran was prepared. Thesolution was applied to a foamed aluminum body by brush application. Thesolvent was allowed to evaporate, leaving a thin coating of ABS resin onthe foamed aluminum.

EXAMPLE 4 A milky appearing so] of polyethylene in butyl alcohol wasprepared by adding polyethylene powder to butanol and stirring themixture. The resultant sol was brushed onto a section surface of foamedaluminum such that the sol flowed into the exposed pores. The butanolwas evaporated, leaving a foamed aluminum body coated on one surfacewith polyethylene.

A plastic layer can be applied to the foamed metal body by cold molding.According to this technique, an organic composition is admixed with aphenolic resin dispersed in a solvent. This is admixed with a fillersuch as asbestos fibers, silica, or magnesia. The resultant mass, wherepossible, is preshaped to the approximate shape of the finished article.Next, the composition and the foamed metal body is put into a mold. Thecomposition and foamed metal substrate is then pressed together underpressure to bond the polymericcontaining material to the foamed metalsubstrate. There is no heating or cooling cycle.

Alternatively, a plastic layer can be applied by hot compressionmolding. This technique is best employed for thermosetting compositions,because theremoplastic materials require cooling before removal of thearticle and preheating before receiving the next charge. This adds toexpense because of the time lost.

In general, the charge and the foamed metal substrate are placed in aheated mold, the mold is closed, generally under low pressure, untilpressure is exerted on the material. The charge becomes plastic andunder increased pressure is forced to fill cavities in the surface ofthe foam substrate. The molded article is kept under pressure untilcured. After that, the mold is opened and the molded part removed.

The charge is usually beads, scraps, granules, or it may be tableted orpreformed. Preforming is advantageous when flow is poor, such as withpolytetrafluoroethylene.

The charge can be preheated prior to insertion in the mold. Electronic,steam, and air preheating are artrecognized methods. Molding is usuallycarried out at l45-380C. More preferably, temperatures from l45-200C.are used. The pressure utilized can be from, say, 300-800 psig.; usuallyit is best to use pressures from 500-5,000 psig. Low pressures can beused while the mold is being closed and higher temperatures can be usedduring molding.

Transfer molding techniques such as those described on pages 587-589 ofGolding, Polymers and Resins, D. Van Nostrand Co., Inc., New York (1959)can be used.

All types of foamed materials can be used as substrates for thisinvention. However, a highly preferred embodiment is plastic-coatedfoamed aluminum. The aluminum can be alloyed with various metals. Thus,it can contain up to about 50 per cent of magnesium, manganese, orcopper. Foamed aluminum containing up to about 10 weight per cent leadalloy therewith is a preferred embodiment because such foamed aluminumshave superior sound-dampening properties.

The following alloys yield foams suitable for this invention when usedin a process employing a titanium or zirconium hydride as a blowingagent. Suitable techniques are the processes of the prior art set forthin the patents cited herein in the section Background of the Invention.Moreover, said alloys yield suitable foams when the molten alloy is mademore viscous by a suitable viscosity-increasing agent.

Alcoa alloy 7075 (1.6 Cu, 2.5 Mg, 0.3 Cr, 5.6 Zn,

remainder Al) 2024 (4.5 Cu, 0.6 Mn, 1.5 Mg, remainder 5086 (0.45 Mn, 4.0Mg, 0.1 Cr, remainder 6063 (0.4 Si, 0.7 Mg, remainder Al) Almag 35 (6-8Mg, in Al) 1,000 series A1 (99.6 minimum A1) 2011 (5.5 Cu, 0.5 Pb, 0.5Bi, remainder 2218 (4.0 Cu, 1.5 Mg, 2 Ni, remainder A1) 3005 (1.2 Mn,0.4 Mg, remainder A1) 4042 (12.2 Si, 0.9 Cu, 1.1 Mg, 0.9 Ni,

remainder Al) 8 4043 5 Si. 95 A1) 8280 (1.5 Si, 1.0 7v Cu. 0.5 7r Ni.remainder Al) Magnalium 70 Al, 30 7: Mg

An especially preferred embodiment is a plastic coated foamed metal bodyin which the foamed metal has a density less than about 38 per cent ofthe density of the same non-foamed metal. For example, aluminum has adensity of about 170 pounds per cubic foot and, hence, in this preferredembodiment, foamed aluminum having a density up to about 65 pounds percubic foot is used. The usefulness of the plastic coated foamed metal isenhanced still further using foamed metals of even less density belowabout 20 pounds per cubic foot.

EXAMPLE 5 The following is a general procedure illustrating preparationof plastic coated metal foams by a hot compression molding technique.

A sample of a foamed aluminum having a density of 10-40 per cent of thedensity of aluminum ingot is employed. Such samples have approximatedimensions of 6 X 2 X 1 inches. At least one of the 6X 2 inches surfacesis characterized by having a pitted" configuration. Such pittedconfiguration can be gained by preparing the sample by making a sectionthrough a foamed aluminum body of said density wherein the pore sizeaverages 1/16 3/32 of an inch and the pore size of, say, per cent of thepores ranges from about V8 inch to about l/64 inch.

From 5-15 grams of Acrylonitrile-butadiene-styrene resin is placed onthe 6 X 2 inch surface above described. (A resin used was Tybrene 27,Natural 7 supplied by Dow Chemical Company. Such plastic is a solid inpellitized form.) Where desired, the pellets are admixed withapproximately 2 per cent by weight of a dye. Dyes found suitable are thefollowing, supplied by Allied Chemical Corporation.

BC 70920 plasto blue G BC 70921 plasto blue RDA BC 70922 plasto green BBC 70923 plasto orange R BC 70924 plasto red B BC 70925 plasto yellowMGS BC 70926 plasto yellow Y The foamed metal substrate, plastic (anddye) are placed in a hydraulic press whose 6 X 6 inch platens havepreviously been heated to 475-500F. The material is so placed in thepress that the plastic (and dye) is on top. Between the top platen andthe pellets is placed a covering sheet of a somewhat heavy gaugealuminum foil, say, 15 mil thick. The press is barely closed, say, toabout 50 pounds per square foot, and allowed to remain in thisconfiguration for about 3-5 minutes. In this manner the hot top platenheats the plastic.

Thereafter, additional pressure can be applied, say, an additional 10-50lbs/sq. foot, to cause the plastic to melt and flow over the entire topsurface of the foamed aluminum. When the entire top surface is coveredwith the plastic, the plastic-coated foam is removed from the press.This yields a plastic-coated foam to which is attached the heavy foil.

This object is then cooled, optionally with water or other coolant suchas dry ice. The aluminum foil can be removed, if desired.

Using about grams of resin on the surface above described yields acoated foam having a thin coat of plastic thereon. ln other words, thetops of the walls of the pore surfaces are visible through the plastic.This gives an aesthetically pleasing effect similar to a cloisonne, withmost of coat embedded into the surface cavities of the foam filling themup to make a smooth surface. Of course, more plastic than 5 grams yieldsa thicker coat on the surface of the metal foam.

The process described above lends itself well to scale-up. Thus, largercoated foamed bodies can be made to order if comparatively largeramounts of plastic (and dye) are employed between larger platens onbigger samples of substrate.

The above procedure has been extended to a thermosetting melamine resin.The platen temperature was 375F. About 5 g of undyed melamine resin wasused and the resultant plastic-coated foam surface was white-gray havinga marble-like appearance.

Similarly, the above procedure was applied to a methacrylate resin whichhad been admixed with a hardener. A clear plastic coat was obtained.

Similarly, a polypropylene coat was laid down using a platen temperatureof 400F.

In the cases where the above technique was employed, the polymericmaterial had filled cavities in the treated surface.

Utilizing the low pressures employed in this example, coated materialswere made from other samples of foamed aluminum in which the cavitieswere larger than those mentioned above. in one instance, the cavities,in general, were from 3/32-5/32 inch in size. Utilizing this material acommensurately greater amount of plastic was employed.

In instances where the above general procedure was employed, visualinspection demonstrates that the cavities in the surface so treated arewell filled with plastic material to depths of the cavities present inthe surface.

For much smaller cavities, it is expedient to increase the compressionand/or temperature pressure to force the plastic to flow into thesmaller pores. Pressures in the range of -200 psig. are advantageouslyemployed. Usually, it is preferred to use a pressure less than thatwhich compresses the foamed substrate, but higher pressures can beemployed if desired to materially alter the treated surface by admixingthe plastic coat with a crushed foamed surface.

EXAMPLE 6 A liquid polyester resin (Michigan Fibreglas Sales, lnc., No.130) was admixed with a hardener (Michigan Fibreglas Sales, lnc., EH No.37) in the ratio of 4 parts resin to 1 part hardener. This was thenspread upon a foamed aluminum sample having a pore size of from about 1/[6 to about 1/32 of an inch as described in Example l. (Brushing,rolling, or spraying are suitable application techniques.) Afterapplication, a fiberglass mat was placed on the resin surface and theresin allowed to harden. After drying, another coat of resin was appliedto the top of the fiberglass. This was allowed to dry and was sanded.Additional layers of resin and fiberglass can be applied before or aftersanding.

The above example illustrates the preparation of a fiber reinforcedplastic coated foamed metal body as shown in FIG. 3. Similar procedurescan be used to prepare other fiber reinforced plastic coatings. A broadrange of fiber reinforcing material can be used such as graphite fiber,fiberglass, Kao-Wool fibers, aluminized graphite fibers, zincatedgraphite fibers, refractory fibers such as potassium titanate, siliconcarbide, alumina,. boron nitride, titanium carbide, titanium oxide,metal coated refractories, and metal fiber such as titanium fiber,nickel fiber, iron fiber, nickel-plated iron fiber, steel fiber,aluminized steel fiber, and the like. Likewise, the technique is readilyapplied to different plastic coatings including epoxy resins,polyurethanes, melamines, ABS, polycarbonates, polyacetals,polyphenylene ethers, and the like. For example, an epoxy resin andhardener can be substituted for the polyester resin used in Example 6 toprepare a foamed aluminum coated with a fiberglass reinforced epoxyresin. The fiberglass need not be in mat form but can be randomfiberglass. Substitution of graphite fiber yields graphite fiberreinforced polyester coated aluminum foam. lf epoxy resin is employedthe product is graphite fiber reinforced epoxy coated aluminum foam.

A useful method of preparing the fiber reinforced plastic coated metalfoam is to lay on the foamed metal surface a sheet of plastic filmpro-impregnated with reinforcing fiber and press the reinforced filmagainst the foamed metal surface. In this embodiment, the plastic filmis preferably an incompletely cured thermosetting resin such as afiberglass of graphite fiber reinforced polyester or epoxy filmcontaining a curing agent. Such pre-impregnated films are availablecommercially (Fiberite (lM) pre-preg. tape, West Coast Corp., Orange,Calif, and Scotch-Weld" (TM) structural film, 3M Company, Minneapolis,Minn.). They are applied to the foamed metal body by placing the fiberimpregnated film on the foamed metal body and pressing it against themetal body while heating it to a curing temperature (300-450F.) untilthe film is cured.

The following example illustrates the preparation of a fiberglassreinforced epoxy coated foamed aluminum.

EXAMPLE 7 On each broad surface of a foamed aluminum (density 16.4pounds per cubic foot) slab (2.5 X 12 X 0.75 inch) was placed a sheet offiberglass cloth impregnated with a thermosetting epoxy laminateadhesive. The slab with the impregnated glass cloth in place was placedbetween the platens of a press. A pressure of psi was applied and theplatens heated to 250F. and held at that temperature for 1 hour. Theywere then cooled and the pressure released. The fiberglass reinforcedepoxy coated aluminum foam was removed. The strength of the coatedfoamed aluminum was greatly increased. This was measured by placing thecoated foamed aluminum slab across a 10 inch span and placing a load atthe center. Uncoated foamed aluminum of this dimension will fail ataround 30 pounds. The foamed aluminum coated with fiberglass impregnatedepoxy did not fail until the load reached 278 pounds, at which point itsdeflection was 2.85 per cent of span.

EXAMPLE 8 This example gives an illustrative general procedure forpreparing a plastic coated metal foam having items embedded in theplastic layer.

Foamed aluminum samples are prepared as in Example l, utilizing -15 g ofABS resin on a 6 X 2 inch foamed metal surface.

Thereafter, the coated material (coated side up) is put back in thepress which has the platens preheated to a temperature which will softenthe plastic coat. A suitable platen temperature is 475-500F.

After the plastic coated material is softened, a material to be embeddedin the plastic coat is placed on the softened surface. Illustrativesubstances are quartz, marble, or enamel chips, crushed rock, metalflakes, wires, or turnings and glass wool, or .beads. Pressure of 10-100pounds per square foot is then impressed, forcing the substance to embedin the coat. Pressure is released and the resultant object allowed tocool.

Using the above procedure, two foamed aluminum bodies can be joined byplacing one body into a softened coat on another body. In this way,plastic is between the butted surfaces. Foamed aluminum bodies can alsobe joined using plastic coats on top, bottom, and/or sides of bothconjoined bodies with plastic between or not present between the buttedsurfaces as desired.

EXAMPLE 9 Some foamed metal samples have a large number of open cellsand/or small imperfections in the walls of apparently closed cells.These allow fluid to penetrate freely from surface cavities into thebody of the foamed metal. Utilizing such samples, plastic coats can beapplied which penetrate to any desired depth in the foamed body.

This is illustrated by the following procedure. A mixture of Polyclear,an acrylic substance supplied by Transene Co., Inc, of Rowley, Mass, ismixed with a hardener as directed by the supplier. If this mixture isimmediately applied to foamed aluminum having small imperfections in thecell walls, the quite fluid mixture will penetrate to about 70 per centof the depth of a 1 inch thick foam before hardening. Alternatively, ifthe mixture is allowed to set up for about minutes before application,the penetration is lessened by -30 per cent.

If the mixture is allowed to set up for longer periods, the penetrationcan be further lessened.

Carvable epoxy coats can be made from slurries of epoxy resins coated onfoamed metals. The epoxy-foam composite can be used for tooling needssuch as for numerical control cutting machines.

A particularly preferred embodiment of the invention is a foamedaluminum body having a density of from about 0.2-1.0 gram per cc (about12-65 pounds per cubic foot) having a surface thereof coated with aplastic coating wherein the plastic has a density of from about 0.9-2.7grams per cc. In this manner, a panel can be made which has all thesurface properties of the plastic coating such as resistance to chemicalattack and water imperviousness, and, at the same time, has strengthgreater than even the foamed aluminum. In order to obtain thiscombination of properties with the plastic alone a much heavier panelwould be required.

Another feature of this particularly preferred embodiment of theinvention is that it enables the manufacturer of articles having aresultant density of less than 1 and having surface properties of aplastic which has a density of greater than 1. Such articles have thedesirable surface properties of the plastic and the high strength of thefoamed aluminum and will float in water. They find applications in areassuch as in the manufacture of surfboards.

The following example illustrates the preparation of a fiberglassreinforced ABS coated foamed aluminum panel.

EXAMPLE 10 A fiberglass mat was placed on a sectioned surface of foamedaluminum. ABS pellets were uniformly distributed over the mat. Aluminumfoil was placed over this and the structure placed between the heatedplatens of a press. A pressure of about 150 psi was applied and theplatens heated to 500F. After 10 minutes, the platens were cooled andthe pressure released, giving a foamed aluminum panel having a surfacecoated with fiberglass reinforced ABS.

A series of fiberglass reinforced polyester and epoxy coated foamedaluminum panels of varying thickness were prepared following theprocedure of Example 7 and their load bearing properties determined. Thepanels were 2.5 X 12 inches and were coated on both broad surfaces witha 32 mil coating. The results were as follows:

l0 Span Failure Load (lbs! Fiberglass Fiberglass Panel ReinforcedReinforced Thickness Bare Foam Polyester Epoxy 0.25" l0 55-60 -90 0.375"l0-l3 80-90 l65-l80 0.50" 20-25 190-240 275-300 0.75" 45-60 315-380495-525 1.00" -110 475-500 680-710 These results demonstrate the largeincrease in load bearing properties of the coated foamed aluminum.

Further tests were carried out relating the load bearing properties ofthe foamed aluminum panel to the thickness of a fiberglass reinforcedpolyester coating. The results with a 0.63 inch thick foamed aluminumpanel 2.5 X 12 inches were as follows:

Coating Thickness 10" Span Failure Load (mils) (lbs.)

5 96-120 l5 l-2l4 25 265-308 32 285-350 50 455-505 64 600-625 ShcctThickness l" Spun Failure Load (mils) (lbs) llO-l25 17 255-278 34580-660 The above results demonstrate the high strength of the plasticcoated foamed aluminum bodies of the present invention.

We claim:

is foamed polystyrene.

1. AS AN ARTICLE OF MANUFACTURE, A FOAMED METAL BODY HAVING A SURFACETHEREOF COATED WITH A FOAMED ORGANO-POLYMERIC PLASTIC OF SUFFICIENTTHICKNESS TO IMPART SHOCK INSULATION PROPERTIES.
 2. An article of claim1 wherein said foamed metal body is foamed aluminum.
 3. An article ofclaim 2 wherein said foamed plastic is foamed polyurethane.
 4. Anarticle of claim 2 wherein said foamed plastic is foamed polystyrene.